Self-fusing flame spray material



United States Patent Oflfice 3,305,325 Patented Feb. 21, 1967 3,305,326 SELF-FUSHNG FLAME SPRAY MATERIAL :Franir Nicholas Longo, Mineola, N.Y., assignor to Metco Ind, Westhury, N.Y., a corporation of New Jersey No Drawing. Filed Apr. 23, 1963, Ser. No. 274,956 Claims. (Cl. 29-192) This invention relates to a self-fusing flame spray mate'- rial and process.

The invention more particularly relates to a sprayweldable, seif-fluxing metal powder which will fuse or weld as flame sprayed, and to such material additionally containing carbides which will allow the flame spraying of carbide coatings.

Spray-weldable, self-fluxing metal powders are well known and Widely used in the art, and are for example described in U.S. Patents Nos. 2,875,043 of February 24, 1959, and 2,936,229 of May 10, 1960. These powders contain a base metal, such as nickel or cobalt, and a metal, such as boron or preferably boron and silicon, to provide fluxing properties. The powders are most frequently used for applying fused coatings to steel or'steel-alloyed bases by a process known as spray-welding. The spray-welding process involves the steps of first spraying the powder onto the surface to be coated by the conventional flame spray process, and thereafter fusing the coating in place. This fusing may be done, for example, in a furnace by means of heating torches applied directly to the coated surface, or by means of induction heating or the like.

The flame spraying in the spray-weld process is simply a mode of positioning the alloyed powder on the surface to be coated in order to allow fused coating to be formed by the subsequent fusing operation. The coating, as sprayed prior to the fusing operation, is porous and not firmly bonded in place and is not useful in the same manner as the subsequent fused coating, i.e. is not a hard, dense, wear-resistant surface.

The spray-weldable, self-fluxing metal powders were often mixed with carbides, such as tungsten carbide, titanium carbide, zirconium carbide, or the like, to produce an even harder, more wear-resistant coating. The flame-sprayed coatings as produced with these carbidecontaining powders, however, could not be ground and finished to as high a surface finish necessary or desirable for many purposes, as for example bearing surfaces. Furthermore, it was not possible to spray extremely thin coatings with these carbide-containing powders, as for example coatings not more than several thousandths of an inch thick, which were useful and desirable for various purposes.

It is an object of this invention to provide a flame spray material which will produce directly upon flame spraying and without a subsequent fusing operation, coatings equivalent to the fused spray-weld coatings.

It is a further object of this invention to provide a flame-spray material containing a carbide which, upon flame spraying, will directly produce a fused, dense coating having alloyed phases harder than ordinary carbide, and which may be ground and finished to a very high surface finish.

A still further object of this invention is to provide a flame-spray material containing a carbide which is selfbonding on flame spraying, and which may be used to produce thinner carbide coatings than could previously be obtained by flame spraying.

These and still further objects will become apparent from the following description.

In accordance with the invention I have discovered that the conventional spray-Weld-able, self-fluxing metal powders may be rendered self-fusing, i.e. will automatically form a fused coating upon flame spraying, without a separate fusing operation, if the same is admixed with powder particles which are coated with a coating material which will exothermically react with the powder nucleus material upon being flame-sprayed, as for example nickelcoated aluminum particles.

I have further discovered that if a refractory carbide is also mixed in the powder, the coatings formed are extremely wear-resistant and contain alloy phases of unexpected hardness. The coatings formed by spraying the carbide-containing powder may furthermore be finished to a high surface finish, and extremely thin coatings, as for example less than several thousandths of an inch in thickness, may be formed.

The starting spray-weld, self-fiuxing powder may be any known or conventional self-fluxing powder, as for example any of the powders described in U.S. Patents 2,875,- 043 and 2,936,229. Preferably the self-fiuxing, sprayweld powders are of the nickel or cobalt type, containing boron and most preferably boron and silicon, as the selffluxing element. The most preferable spray-welclable, self-fluxing metal powders are of the nickel or nickelchrornium alloy type containing boron and silicon. In addition to the base metal, i.e. the nickel and/or cobalt, and the fluxing element, which is the boron or boron and silicon, the powder may be formed of additional alloy components, as for example up to 20% chromium, to impart corrosion and oxidation-resistance, carbon in the amount of not more than a few percent, iron in an amount not exceeding about 10% and preferably 5% by weight of the total alloy. A typical spray-weldable alloy of the boron nickel type of which the powder is composed may, for example, consist of 0.7 to 1% carbon, 3.5 to 4.5% silicon, 2.75 to 3.75% boron, 35% iron, up to 18% chromium, as for example 16 to 18% chromium with nickel making up the balance.

A typical spray-weld alloy of the cobalt-base type may, for example, contain from 1 /2 to 3% boron, 0 to 4.5% silicon, 0 to 3% carbon, 0 to 20% chromium, 0 to 30% nickel, 0 to 20% molybdenum, 0 to 20% tungsten, and the balance cobalt.

The powder should not generally have a mesh size above about U.S. Standard screen size, with the exact size depending upon the particular equipment used for spraying and the particular fuel gas. For example, when intended for spraying with a plasma flame, the particles should be of a size between 100 mesh to +8 microns, and preferably between 270 mesh to +15 microns. For use with acetylene the particles should all be below about mesh U.S. Standard screen size, with not more than 15% below 325 mesh. When intended for spraying with hydrogen as the fuel gas, the lower limit is about 5 microns, and all the particles may be below 325 mesh.

The powder particles which are coated with a material which will exothermically react therewith during the flame spraying, are metal particles containing a coating of another metal which will exothermically react with the first mentioned metal at the flame spray temperatures, to form an intermetallic compound liberating heat. Such particles may consist of any two metals (one forming the nucleus and the other the coating) which are capable of combining at the spraying temperatures to form an intermetallic compound, and in which the intermetallic compound formation involves an exothermic reaction. Examples of such particles include particles in which one of the components, i.e. the nucleus or the coating, is aluminum and the other is any of nickel, antimony, calcium, cobalt, chromium, lanthanum, lithium, manganese, palladium, praseodymium dysprosium, or a combination thereof. The most preferable powder has been found to be aluminum powders which are coated with nickel. The coating on the nucleus metal may be formed in any known or conventional manner, as for example, chemical plating; the deposition of the metal from a solution by reduction on a seed or nucleus, such as the hydrogen reduction of ammoniacal solutions of nickel and ammonium sulphate on a seed powder catalyzed by the adidtion of anthraquinone; vapor deposition; the thermal decomposition of metal carbonyls; hydrogen reduction of metal halide vapors; thermal decomposition of halides, hydrides, carbonyls, organo-metals or other compounds, or by displacement, gas-plating or the like. The relative amounts of the nucleus and coating metal in the coated particles should preferably correspond to the amounts in the intermetallic to be formed in the exothermic reaction. Thus, for example, in connection with nickel-coated aluminum particles, the same should contain about 16 to 18% by weight of aluminum and 84 to 82% by weight of nickel. Metal particles coated with a further metal, which can exothermically react therewith to form an intermetallic compound, are described in copending application, Serial No. 134,544 filed August 16, 1961, now Patent No. 3,254,970 and any of the exothermically reacting clad powders described in said application may be used herein. 1

The particle size of the coated particles should be similar to that of the spray-weld alloy powder and should be between about 170 to +270, and preferably 200 to +270 mesh US. Standard screen size.

The powder mixture in accordance with the invention should contain about 550%, and preferably -20% by weight, of the exothermically reacting coated particles, the balance being the spray-Weldable, self-fiuxing metal powder.

The powder mixture in accordance with the invention is preferably sprayed with a plasma flame spray gun in the conventional manner, and the conventional and conventionally available plasma flame spray guns may be used for this purpose. These guns may, for example, produce their plasma flame in the manner described in US. Patent No. 2,960,594, and nitrogen or argon alone or admixed with hydrogen may be used as a plasma-forming gas.

It is also possible to spray the powder mixturesin accordance with the invention with the conventional powder-type flame spray guns, utilizing for example acetyleneoxygen or hydrogen-oxygen as the fuel gases. latter combustion flame-type guns, however, the coating formed is not as dense as the coating obtained with plasma flame spraying.

Coatings may be formed on conventional surfaces, as for example iron and steel alloy surfaces, for the conventional purposes. Thus, for example, coatings of a depth between .002" and .050", and preferably .010" to .025, may be formed which are useful, for example in pump seals, cultivator blades, gun stocks, templates, glass mold plungers, bearings, or any other application where a fused coating would normally be used.

The coating, as flame-sprayed and particularly when plasma-sprayed, automatically fuses in place and a separate fusion step is not required. The coatings as sprayed are substantially comparable to the coatings produced with the conventional, self-fluxing alloys sprayed in the conventional manner and thereafter fused.

In addition to spraying the powder mixture in accordance with the invention per se, the same may be sprayed in admixture with other components.

In accordance with a preferred embodiment of the invention it has been found that if the powder mixture in accordance with the invention additionally contains a refractory carbide, such as tungsten carbide, titanium carbide, zirconium carbide, tantalum carbide, columbium carbide, hafnium carbide, chromium carbide or the like, extremely high quality coatings are produced, which are superior in various respects to the conventional carbide coatings.

The carbides used in accordance with this embodiment should have a particle size between about -140 mesh With these at. US. Standard screen size and 8 microns, and preferably between about -270 mesh and +15 microns, with the amount of carbide being between about 1075% and preferably 45-55% by weight, based on the total powder mixture.

If the refractory carbide powder is in a form so that the refractory carbide is bound in a matrix, as for example a cobalt or nickel matrix containing 520% by weight of either cobalt or nickel, unusually hard and wear-resistant coatings will be produced which do not contain the individual carbide particles imbedded'in a fused matrix, but instead contain alloy phases whose micro-hardness is actually substantially higher than that ordinarily obtained from a bonded carbide.

When the powder, in accordance with the invention, containing this matrix-bonded refractory carbide is plasma-sprayed, the same automatically fuses in place and is self-bonding, so that the conventional surface preparation for flame spraying, as for example a deep surface roughening, is not required. The coatings produced furthermore may be ground and finished to a very high surface finish, as for example 5 micro inches or even finer, as compared to conventional values of 30 or 40 micro inches, which are the best that could be produced in connection with the carbide-containing, flame-sprayed coatings, unless such coatings were subsequently fused.

Furthermore, extremely thin coatings may be produced, as for example between .001 and .002 thick. If, for example, such a coating is applied to one side of a knife blade, a wear-resistant, self-sharpening knife edge is produced.

The carbide coatings formed in accordance with the above are extremely hard and wear-resistant, and may be useful as bearing surfaces, abrasive surfaces, corrosion barriers, and for any other purpose wherein a working surface requires thin, non-porous, extremely wearresistant coating.

While as mentioned extremely thin coatings with as thin as .001 may be formed, it is also possible to form thicker coatings, as for example as thick as .03" and even thicker.

It is also possible, in accordance with the invention, to incorporate the refractory carbide in the powder in such a manner that the fused coating formed will consist of a fused matrix containing individual carbide particles. For this purpose the refractory carbide, preferably, should not be matrix-bound, but should be a pure crystalline carbide, also having the particle size and used in the amounts indicated above. The crystalline carbide-containing coatings'formed in accordance with the invention will have extremely high wear-resistance due to the carbide particles, which are dispersed and tightly bound in the fused coating. Coatings may be used for the same type of applications as mentioned in connection with the coatings formed with the matrix-bound carbide.

The following examples are given by way of illustration and are not limitations:

Example 1 An aluminum powder having a particle size between l40 mesh and +325 mesh (U.S. Standard screen size) is coated with nickel in the known manner by the hydrogen reduction of an ammoniacal solution of nickel and ammonium sulphate, using anthraquinone as the coating catalyst. The reduction is effected at a temperature between about 300 and 350 F. in a mechanically agitated autoclave, using solutions containing 40-50 grams per liter of nickel and 10-400 grams per liter of (NH SO and 20-30 grams per liter of NH About .2 gram per liter of anthraquinone is used as the catalyst and the auto clave is pressurized with hydrogen at a pressure of about 300 lbs. p.s.i. After the nickel solution is depleted and the aluminum coated with an initial coating of nickel, the solution is discharged from the autoclave and replenished with a fresh solution which need not contain further amounts of the anthraquinone coating catalyst, as the initially formed nickel coating in itself acts as a catalyst. The cycle is continuously repeated until a composite powder is formed containing about 16 to 18% by weight aluminum and 84 to 82% by weight nickel. and a size of 100 to +270 mesh.

The nickel-coated aluminum powder thus formed is ad mixed with a self-fluxing, spray-weld alloy of a particle size between 270 to having the following nominal composition: C, 1.0; B, 3.5; Si, 4; Fe, 4; Cr, 17; Ni, balance; so that the mixture contains 15% of the nickelco-ated aluminum, the balance being the self-fiuxing, sprayweldable powder. The powder mixture is then flamesprayed on a mild steel plate which has been surfacecleaned with emery cloth. Spraying is effected at a distance of about 46 from the plate, using the plasma flame spray gun sold by Metco, Inc. of Westbury, Long.

Example 2 In place of the nickel-coated aluminum particles, cobaltcoated aluminum, chromium-coated aluminum or any of the exothermically reacting composites may be used.

Example 3 A powder of the following composition was sprayed at a distance of 35" in the identical manner described in Example 1:

50% by weight of 12% cobalt-bonded tungsten carbide of a particle size between 270 mesh and +15 microns;

35% by weight of a spray-weldable, self-fluxing metal powder having a particle size between -270 mesh and +15 microns, and having a composition of Percent Carbon 1 Boron 3 .5

Silicon 4 Iron 4 Chromium 1 7 Nickel, balance.

15% by weight of the nickel-coated aluminum described in Example 1, having a particle size between 200 and 270 mesh.

A self-bonded, self-fused, pore-free, wear-resistant carbide coating of .003" thickness was formed. This coating contained alloyed phases of tungsten carbide and cobalt, with a micro-hardness of KHN 3,000. This compares to a hardness of KHN 2,500 of the usual tungsten carbide in a 12% cobalt matrix.

Example 4 In place of the 12% cobalt-bonded tungsten carbide, crystalline tungsten carbide may be used, in which case the fused coating contained dispersed particles of crystalline tungsten carbide.

Example 5 Examples 3 and 4 may be repeated, using in place of the tungsten carbide, titanium carbide, zirconium carbide, tantalum carbide, columbium carbide, hafnium carbide, and chromium carbide.

Example 6 Example 3 may be repeated, using in place of cobalt,

nickel or nickel alloy as binder for the carbide.

In the examples, in place of the specific spray-weldable,

. 6 self-fluxing metal powder described, any of the powders set forth in US. Patents 2,875,043 and 2,936,229 or any other conventional spray-weldable, self-fiuxing metal powders may be used.

While the invention has been described in detail with reference to certain specific embodiments, various changes and modifications which fall within the spirit of the invention and scope of the appended claims, will become apparent to the skilled artisan. The invention therefore is only intended to be limited by the appended claims or their equivalents, wherein I have endeavoured to claim all inherent novelty.

I claim:

1. A powder mixture for flame-spraying comprising a boron containing nickel or cobalt spray-weldable, selffluxing metal powder and coated powder particles comprising a metal nucleus and coating of a metal capable, at flame-spray temperatures, of exothermically reacting with the metal nucleus to form an intermetallic compound, said coated powder particles being present in amount of 5 to 50% by weight of the mixture thereof with the self-fluxing powder.

2. A powder mixture according to claim 1 in which said coated powder particles are present in amounts of 1020% by weight of the mixture thereof with the selffiuxing powder.

3. A powder mixture according to claim 1 having a particle size below 100 mesh.

4. A powder mixture for flame-spraying comprising a boron containing nickel or cobalt spray-weldable, selffluxing metal powder and nickel-coated aluminum powder particles, said nickel coated aluminum particles being present in amount of 5 to 50% by weight of the mixture thereof with the self-fluxing powder.

5. A powder mixture according to claim 4 in which the nickel-coated aluminum particles are present in amounts of 10 to 20% by weight of the mixture thereof with the self-fiuxing powder.

6. A powder mixture according to claim 4 having a particle size below 100 mesh.

7. A powder mixture according to claim 4 in which said nickel-coated aluminum powder particles contain about 16 to 18% by weight of aluminum, and 84 to 82% by weight of nickel.

8. A powder mixture for flame-spraying comprising; (a) boron containing nickel or cobalt spray-weldable, self-fluxing metal powder; (b) coated powder particles comprising a base metal nucleus and a coating of a metal capable, at flame-spray temperatures, of exothermically reacting with the base metal to form an intermetallic compound, and (c) refractory carbide particles of the group consisting of tungsten carbide, titanium carbide, zirconium carbide, tantalum carbide, columbium carbide, hafnium carbide and chromium carbide, (b) being present in amount of 5 to 50% by weight of the mixture thereof with (a), (0) being present in amount of 10 to by weight of the mixture thereof with (a) and (b).

9. A powder mixture according to claim 8 in which said coated powder particles are present in amounts of 10 to 20% by weight of the mixture thereof with (a).

10. A powder mixture according to claim 8 in which said refractory carbide is tungsten carbide.

11. A powder mixture according to claim 8 in which said refractory carbide is bound in a matrix selected from the group consisting of cobalt and nickel, said matrix being present in amount of 5 to 20% by Weight of the total carbide and matrix.

12. A powder mixture for flame-spraying comprising; (a) boron containing nickel or cobalt spray-weldable, self-fiuxing metal powder, b) nickel-coated aluminum powder particles, and (c) refractory carbide particles of the group consisting of tungsten carbide, titanium carbide, zirconium carbide, tantalum carbide, columbium carbide, hafnium carbide and chromium carbide, (b) being present in amount of 5 to 50% by weight of the mixtures 7 thereof with (a), (0) being present in amount of 10 to 75% by weight of the mixture with (a) and (b).

13. A powder mixture according to claim 12 in which the nickel-coated aluminum particles are present in amount of 10 to 20% by weight of the mixture thereof 5 with (a).

14. A powder mixture according to claim 12 in which said nickel-coated aluminum powder particles contain about 16 to 18% by weight of aluminum and 84 to 82% by weight of nickel.

15. A powder mixture according to claim 12 in which said refractory carbide is tungsten carbide bound in a matrix selected from the group consisting of cobalt and (I) nickel, said matrix being present in amount of 5 to 20% by weight of the total carbide and matrix.

References Cited by the Examiner UNITED STATES PATENTS 2,936,229 5/1960 Shepard 75170 3,049,435 8/ 1962 Shwayder 11722 3,050,409 8/1962 Bayer 11722 3,053,610 9/1962 Shichman 117-105 10 DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

R. O. DEAN, Assistant Examiner. 

1. A POWDER MIXTURE FOR FLAME-SPRAYING COMPRISING A BORON CONTAINING NICKEL OR COBALT SPRAY-WELDABLE, SELFFLUXING METAL POWDER AND COATED POWDER PARTICLES COMPRISING A METAL NUCLEUS AND COATING OF A METAL CAPABLE, AT FLAME-SPRAY TEMPERATURES, OF EXOTHERMICALLY REACTING WITH THE METAL NUCLEUS TO FORM AN INTERMETALLIC COMPOUND, SAID COATED POWDER PARTICLES BEING PRESENT IN AMOUNT OF 5 TO 50% BY WEIGHT OF THE MIXTURE THEREOF WITH THE SELF-FLUXING POWDER. 